The present invention relates to a plasma display device and a method of producing the same, and particularly to a plasma display device having a characteristic feature as to the material of a dielectric layer formed on a sustaining electrode, and a method of producing the same.
As image display devices to be used in place of the cathode ray tube (CRT) which is the main stream at present, a variety of plane surface type (flat panel type) display devices have been investigated. As such a plane surface type display device, there may be mentioned the liquid crystal display device (LCD), the electroluminescence display device (ELD) and the plasma display device (PDP). Among others, the plasma display device has the merits of comparative easiness in enlarging screen and angle of visibility, excellent resistance to environmental factors such as temperature, magnetism, vibration, long useful life and the like, and is expected to be applied to domestic wall-hung television sets and large size public information terminal equipments.
The plasma display device is a display device in which a voltage is impressed on discharge cells comprising a discharge gas comprised of a rare gas sealed in discharge spaces, and phosphor layers in the discharge cells are excited by ultraviolet rays generated based on glow discharge in the discharge gas to thereby achieve light emission. Namely, the individual discharge cells are driven by a principle similar to that of fluorescent lamps, and, generally, hundreds of thousands of discharge cells are aggregated to constitute a single display screen. The plasma display devices are classified largely into the direct current driving type (DC type) and the alternating current driving type (AC type) according to the system of impressing the voltage on the discharge cells, and both types have respective merits and demerits.
The AC type plasma display device is suitable for enhancing the fineness because the partition walls for partitioning the individual discharge cells in the display screen may be provided, for example, in stripes. Moreover, since the surfaces of the electrodes for discharge are covered with a dielectric layer, there is the merit that the electrodes are worn with difficulty and the useful life is long.
In the AC type plasma display device commercialized at present, a dielectric layer is formed on sustaining electrodes provided on the inside surface of a first substrate, and the dielectric layer is generally comprised of silicon oxide formed by printing a paste followed by firing. In the AC type plasma display device, electric charges are accumulated in the dielectric layer, and are discharged by impressing a reverse direction voltage on the sustaining electrodes, thereby generating a plasma.
However, in the AC type plasma display device in which the dielectric layer is formed by the paste printing method, there are problems as to lightness and light emission efficiency. To cope with this, there is proposed a method of forming the dielectric layer such as silicon oxide by a vacuum film forming method such as a sputtering method, an evaporation method, a chemical evaporation (CVD) method and the like.
However, in the AC type plasma display device according to the prior art in which the dielectric layer comprised of silicon oxide is formed by the vacuum film forming method, there is a problem of voltage resistance characteristic of the dielectric layer for display discharge resulting in occurrence of abnormal discharge. In addition, even if the abnormal discharge is not generated, there is a problem that the discharge becomes instable and reliability is low.
Accordingly, it is an object of the present invention to provide a plasma display device which is excellent in voltage resistance characteristic, in which abnormal discharge would not easily be generated even if the thickness of the dielectric layer is reduced, and which is excellent in discharge stability, durability and reliability, and a method of producing the same.
In accordance with one aspect of the present invention, there is provided a plasma display device comprising: a first panel provided with discharge sustaining electrodes and a dielectric layer on the inside thereof; and a second panel laminated on the first panel so as to form discharge spaces on the inside, wherein the dielectric layer comprises a silicon oxide layer having a density of not less than 6.1xc3x971022 atoms/cm3.
Preferably, the density of the silicon oxide layer is not less than 6.4xc3x971022 atoms/cm3. The upper limit of the density of the silicon oxide layer is not particularly limited, and a higher density is more preferable; the density of quartz crystal is the upper limit.
In the present invention, the dielectric layer is preferably comprised of a single silicon oxide layer, but may have a multi-layer structure. In that case, it suffices that at least one layer in the multiple layers is the silicon oxide layer.
The thickness of the silicon oxide layer is not particularly limited, and is, generally, 1 to 20 xcexcm, preferably, 1 to 10 xcexcm.
The plasma display device according to the present invention is an alternating current driving type plasma display device, in which it is preferable that address electrodes, partition walls in a stripe form for partitioning discharge spaces, and phosphor layers disposed between the partition walls are provided on the inside of the second panel.
In the plasma display device according to the present invention, the dielectric layer has the silicon oxide layer having a density of not less than 6.1xc3x971022 atoms/cm3, so that the voltage resistance characteristic of the dielectric layer is enhanced, abnormal discharge in the discharge spaces is prevented, and the durability and reliability of the device are enhanced.
In accordance with another aspect of the present invention, there is provided a method of producing a plasma display device comprising a first panel provided with discharge sustaining electrodes and a dielectric layer on the inside thereof, and a second panel laminated on the first panel so as to form discharge spaces on the inside, wherein a silicon oxide layer having a density of not less than 6.1xc3x971022 atoms/cm3 is formed at the time of forming the dielectric layer.
The method of forming the silicon oxide layer having a density of not less than 6.1xc3x971022 atoms/cm3 is not particularly limited, and examples of the method include a sputtering method, a chemical evaporation (CVD) method, an evaporation method and the like.
Where a sputtering method is used as the method of forming the silicon oxide layer, film formation by the sputtering method is preferably so carried out that the concentration of oxygen gas in the atmosphere gas introduced into the sputtering apparatus is 5 to 30 vol %. Where the volume ratio of oxygen is too low, it tends to be difficult to obtain a silicon oxide layer having a high density. On the other hand, where the volume ratio of oxygen is too high, it tends to be difficult to achieve film formation.
As the atmosphere gas, a gas containing an inert gas such as argon gas as a main component is used. Where the argon (Ar) gas is used as the inert gas, the volume concentration of oxygen (O2) in the atmosphere gas is represented as O2/(Ar+O2).
Where an evaporation method is used as the method of forming the silicon oxide layer, film formation by the evaporation method is preferably carried out while introducing not less than 1xc3x9710xe2x88x923 Pa of oxygen into the evaporation apparatus. When the quantity of oxygen introduced is too small, it tends to be difficult to obtain a silicon oxide layer having a high density. On the other hand, when too much oxygen is introduced, it is difficult to achieve evaporation by the evaporation method; therefore, the upper limit of the quantity of oxygen introduced is determined within the range in which evaporation is possible.
According to the present invention, a plasma display device can be realized which has a high voltage resistance characteristic, in which abnormal discharge would not easily be generated even if the thickness of the dielectric layer is decreased, and which is excellent in discharge stability, durability and reliability.